1. Field of the Invention
This invention relates to a sheet conveyance apparatus for conveying sheets in use of a rotary member, an image forming apparatus having the sheet conveyance apparatus, and a rotary member lifetime estimation method for estimating duration of the rotary member.
2. Description of Prior Art
In image forming apparatuses for forming images on sheets, a roller made of a rubber material is widely used as a rotary member for conveying sheets with a sheet conveying means such as a sheet feeding section or sheet conveying section for conveying sheets. The roller made of the rubber material, however, shows a wearing phenomenon such as reduction of the roller radius from the property or reduction of the frictional coefficient to the sheet, due to wear of the surface as conveying sheets more. When the roller is worn further, the conveyance efficient of the roller is lowered gradually, and then, it becomes difficult to supply the sheets with a predetermined interval to the image forming area, thereby generating jamming due to delay.
If the roller is continuously used without replacing the roller until a circumstance that the jamming due to delay likely occurs, the user is finally forced to operate the image forming apparatus not properly, and therefore, a system is needed in which necessity of the replacement is detected in advance and the serviceman can come to care the roller. To conventionally realize this, mainly used were two methods: a method in which a counter for counting the number of sheets passing is utilized, and a method in which a conveying timing for sheets is used.
In the former, an estimated total conveyable distance of the sheets until when the roller reaches the end of the lifetime is stored in a memory on a controller, and a signal is outputted for informing nearness of the roller's duration at a stage a little before the accumulated conveyance distance of the roller calculated from the passing sheet number information counted with the counter and from the size information of the actually passing sheets, reaches the total conveyable distance registered in the memory on the controller.
In a meantime, the latter is a system in which the passing timing of the sheets is always monitored with a sheet detection sensor formed on a sheet conveyance route, and if the timing is delayed more than a certain amount according to wear on the roller, it is judged as that the duration of the roller comes closer to the end, and a warning signal is outputted.
In those duration detecting methods, theoretically, any trouble due to wear on the roller can be prevented, and the roller can be replaced before such a trouble occurs.
With those duration detecting methods, however, although the system can inform that “it is close to the end of the roller's duration based on the accumulated conveyance distance” or can detect the fact that “the conveyance efficiency on the roller is lowered to the predetermined value,” the system cannot estimate “when the roller reaches the end of the duration.” This is because it is impossible to guarantee a fixed total conveyable distance for rollers in all products, and the period reaching the end of the duration cannot be constant, since the wearing degree on the roller depends on various factors such as installation circumstances around the apparatus at a place of the use, types of the used sheets, use frequency of the apparatus, etc. Therefore, the conventional duration detecting methods could not correspond flexibly to the use circumstance of the apparatus, and also, it was difficult to judge which user has to receive the maintenance work with priority, so that the services tend to loose efficiency, and so that some problem was raised in which the replacement was not in time.